Pitney Bowes MapInfo Vertical Mapper - Manual (Page 38)

Inverse Distance Weighting Interpolation
36
Vertical Mapper 3.7
The search area is divided into two zones and a zone orientation set to match the
distribution of the data points. This forces Vertical Mapper to use data points from two
different sample paths when estimating grid values that lie between paths. The
minimum and maximum number of points settings apply for each zone. In this figure,
the zone orientation is set to 45 degrees.
The Radius Multiplier box enables you to define a weighting factor that determines the degree of
influence of neighbouring points that lie successively farther from the grid node. A radius multiplier of
one means a point located at the edge of the search radius has a weight of zero in the averaging
calculation. A radius multiplier of two has the effect of doubling the distance used for weighting the
points. Increasing the radius multiplier value is a way of increasing each point’s influence on the
calculation of a grid node without increasing the size of the search radius.
When the radius multiplier is set to one and the search radius at SR1, the data point
will have the amount of influence, represented by A, on the grid node value. If the
radius multiplier is set to two (two times the search radius distance, SR2), the data
point will have an increased amount of influence represented by B. Only points within
SR1 will be selected and used in the grid node calculation; however, the amount of
influence they have can be controlled by the radius multiplier.
The Weight to Furthest Point Only check box enables you to apply a decay curve (exponent)
based on the distance to the farthest point used in the calculation. This point is defined by the
Maximum # of Points setting.